Many bicameral states started with different ways to elect the chambers. In some the Senate reflected the counties, much as the US Senate reflected the states. Since the one-man-one-vote decisions of teh 1960's, the state legislative chambers were forced to to be elected on equal population ending any distinctions in that regard.
I've always wondered the same thing, and I think you were the one that mentioned the same back then. It's probably the explanation that makes the most sense.
I think the more interesting question is why no state has attempted to overhaul state government. Some of that, I'm sure, is due to the inertia against change and for incumbency. I do recall some states in recent years having proposals to go unicameral. I'd like to see a state adopt a more radical change (such as California) and go for a unicameral Parliamentary system. Considering the size of the seats in the State Senate in California, bicameralism is pretty ridiculous at this point.
